Practice question

Mechanism of antisense inhibition involves sequence-specific RNA-RNA interaction rather than protein-DNA binding. Transgene transcribes RNA identical to non-coding strand, complementary to mature messenger RNA of target gene. Inside nucleus or cytoplasm, antisense strand anneals to sense mRNA forming double-stranded duplex covering ribosome binding site or coding region. Duplex sterically blocks 40S ribosomal subunit scanning, preventing translation initiation. Additionally double-stranded RNA structure recruits RNase III like enzymes and RNA-induced silencing complex, leading to endonucleolytic cleavage and degradation of target mRNA, reducing steady-state transcript level. No alteration of genomic DNA or transcription factor function occurs. Inhibition dose dependent on antisense transcript abundance driven by strong promoter and stability. Length of complementarity at least 100 nucleotides ensures specificity. This duplex formation with mRNA explains why antisense technology effectively suppresses genes like polygalacturonase without modifying coding sequence itself, forming basis for early transgenic improvement strategies before RNAi discovery popularized double-stranded RNA mediated silencing. Experimental validation includes northern blot showing reduced target mRNA abundance and western blot reduction of corresponding protein after antisense expression. Sense-antisense ratio required for effective inhibition often 10 to 1. In plants, trans-acting small RNAs may amplify silencing, linking antisense mechanism to broader post-transcriptional gene regulation network central to